Without limiting the scope of the present disclosure, its background will be described in relation to forming a window in a casing string for a multilateral well, as an example.
In multilateral wells, it is common practice to drill a branch or lateral wellbore extending outwardly from an intersection with a main or parent wellbore. Typically, once the parent wellbore casing string is installed and the parent wellbore has been completed, a whipstock is positioned in the parent wellbore casing string at the desired intersection and then a rotating mill is deflected laterally off the whipstock to form the window through the parent wellbore casing sidewall, enabling subsequent drilling and completing of the lateral wellbore. In some installations, the mill assembly and the whipstock may be run downhole together as a unit. In such installations, the mill assembly may initially be attached to the whipstock face with one or more shear bolts. Once positioned in the desired location, for example after a latch assembly associated with the whipstock is anchored into and rotationally oriented within a latch coupling interconnected in the parent wellbore casing string, the mill assembly may be separated from the whipstock responsive to compressive shearing.
In certain well configurations, however, such as wells having a tight dog leg or extended reach horizontal wells, it has been found that significant friction is introduced into the well system, which greatly affects the surface load required to compressively shear the shear bolts coupling the mill assembly to the whipstock face. In such configurations, it may therefore be difficult to determine the desired strength for the shear bolts to enable proper installation, separation and operation of the mill assembly and the whipstock. Accordingly, a need has arisen for a system and method for determining the losses associated with a downhole in well system having, for example, a high friction configuration.